Agglomerated anhydrous fructose and process for its production

ABSTRACT

AGGLOMERATED ANHYDROUS FRUCTOSE WHICH IS QUICK DISSOLVING YET NON-HYGROSCOPIC, COMPRISING RELATIVELY COARSE PARTICLES IN TURN COMPOSED OF AGGLOMERATED FINER PARTICLES, IS PRODUCED BY MOISTENING FINE FRUCTOSE CRYSTALS OBTAINED CONVENTIONALLY BY RECRYSTALLIZATION WITH FROM 3 TO 10 WEIGHT PERCENT, BASED ON THE WEIGHT OF FRUCTOSE, OF A 1 TO 4 CARBON ATOM ALCOHOL AND WITH FROM .03 TO 1.5 PERCENT BY WEIGHT OF WATER, BASED ON THE WEIGHT OF FRUCTOSE, AND DRYING THE MOISTENED FRUCTOSE AT FROM 40 TO 90*C.

United States Patent Oflice 3,684,573 Patented Aug. 15, 1972 r 3,684,573 AGGLOMERATED ANHYDROUS FRUCTOSE AND PROCESS FOR ITS PRODUCTION Hans Voigt, Georg Stoeck, Werner Gosewinkel, and

Theodor Kusch, Mannheim-Waldhof, Germany, assignors to Boehringer Mannheim GmbH, Mannheim, Germany No Drawing. Filed Feb. 10, 1970, Ser. No. 10,298

Claims priority, application Germany, Feb. 25, 1969, P 19 09 316.4 US. Cl. 127-30 11 Claims ABSTRACT OF THE DISCLOSURE The present invention is concerned with providing an anhydrous, crystalline fructose in a friable and readily soluble form. In addition this invention relates to a process for the production of such fructose which, because of its simplicity and the ease with which it can be carried out, and because of the quality of the product thereby obtained, is superior to previously known processes.

Modern methods of working 'up fructose, especially in automatic filling machines, require that the fructose remain friable, even after comparatively long periods of storage. Furthermore, the fructose must be in a form rendering it readily soluble, in order to avoid delays in the final working up thereof. In the case of conventional purification by recrystallization from lower alcohols, preferably from methanol, there are obtained, depending upon the process conditions, either readily soluble fine crystals which have, howeverya tendency to become lumpy, or coarse crystals which are readily friable but which, because of the small surface area in comparison with the volume, are difficult to dissolve.

We have now, surprisingly, found that by use of this invention it is possible to obtain a friable and storagestable product from the fine crystalline fructose obtained by the usual recrystallization from anhydrous methanol, while at the same time retaining its quick-dissolving properties.

The process of this invention comprises, essentially, moistening the fine fructose crystals, obtained conventionally by recrystallization, with from 3 to weight percent, based on the weight of fructose, of an alcohol containing up to 4 carbon atoms, and with from 0.03 to 0.5 percent by weight of water, preferably from 0.1 to 1 percent, based on the weight of fructose.

Suitable alcohols are readily water-miscible, low boiling alkanols having from one to four carbon atoms such as methanol, ethanol, n-propanol, isopropanol, n-butanol, tert.-butanol, and isobutanol. Preferred, because of its low cost, availability, desirable properties (e.g., low boiling point) and especially efiicacious performance in the process of the invention, is methanol.

When the thus-moistened fructose is subsequently dried in a conventional drying apparatus at a temperature of 40-90 C., preferablyof 70-80 C., at atmospheric pressure and with circulating air, agglomerates are obtained with a particle size of about 0.2-2 mm., which have the properties desired for the further working up of fructose.

The particle size of the agglomerate can be varied within the above-given limits by variation of the water content during the moistening step and by choice of the conditions maintained during the drying, for example, the temperature of the material to be dried, the nature of the movement of the material during the drying process, and the temperature, relative humidity and amount of the air used for drying. If desired, narrower fractions of optimum. particle size can be separated off by subsequent sieving.

Thus, in one aspect thereof, the present invention provides agglomerated fructose consisting of microcrystalline fructose units with a size of from 10-200 microns, preferably of from 30-100 microns, the agglomerated particles having a size of 0.2-2.0 millimeters, preferably of 0.3-1.0 millimeter.

It' has been found that the use of water instead of the water-containing alcohols used in this invention, does not result in producing the desired agglomerated fructose. On the contrary, by using water there are obtained hard, large lumps, together with unchanged fine crystals, which substantially hamper the further working up of the fructose.

Surprisingly, however, we have found that, in a very simple manner, there is obtained an agglomerate which is not only suitable for further working up but also for storage when, to the amount of water used for dissolving the fructose (0.03-l.5 percent by weight, based on the fructose), there is also added a readily water-miscible, low boiling alcohol containing up to 4 carbon atoms (in an amount of from 3-10%, also based on the weight of the fructose). Especially good results are obtained when the amount of water is maintained between 0.1 and 1.0 percent by weight, based on the fructose.

The amount of alcohol used is not narrowly critical but, when using more than 10 percent of alcohol, the resultant solution no longer adheres completely to the remaining crystals, which results in difiiculties when transferring the material to the drying apparatus. Furthermore, it is also uneconomic, for example, from the point of view of recovering the solvent, to have to evaporate off unnecessarily large amounts of solvent during the drying step. In the case of less than 3 percent of alcohol, the mixing time must be increased in order to ensure a uniform moistening and this is also uneconomic. If the added amount of alcohol is still further reduced, e.g., below about 2 percent, then the uniform moistening which is necessary for the process according to the present invention can no longer be achieved and there are obtained the above-mentioned hard lumps, together with unchanged fine crystals.

The amount of water added is critical and must be maintained between the limits set forth above, because at below 0.03 percent of added water agglomeration is no longer obtained and at above 1.5 percent of added water, too much fructose goes into solution, especially at elevated temperatures, because of the ready solubility of the fructose. In this latter case, hard lumps are again formed which are diflicult to work up further.

The lower limit of the temperature to be used for the drying is determined by the rate of evaporation of the alcohol but, in the case of drying in a vacuum, it can be near or at the lower limit of the above-mentioned temperature range of 4090 C. The upper limit of C. is imposed by the instability of fructose at elevated temperatures and it is preferable to remain at least 10 C. below the maximum. Because of its low boiling point, it is especially economical to use methanol as the alcohol.

According to a preferred feature of the process according to the present invention, it has proved advantageous to move or roll around the mixture during the drying step. This can be carried out, for example, with conventional plate driers, rotating drums or in a fluidized bed. The agglomerates obtained in this manner have a spheroidal surface and are more uniform in size than those previously known, which is advantageous for packing and for further working up.

The process according to the present invention can be carried out especially economically when there are used the moist centrifuged crystals obtained directly from the crystallization of fructose, which contain sufficient aqueous alcohol and can be further worked up under drying conditions of the process according to the present inven tion.

Surprisingly, the fructose produced by the process according to the present invention, especially under the preferred conditions, has excellent properties for further working up and/or storage. It was to have been expected that the agglomerate, if the crystal lattice was loose enough to permit a rapid penetration of water and thus a rapid dissolving, would also possess an undesired property of readily-soluble fine crystals, namely, that it would be hygroscopic. On the other hand, it was to have been assumed that a compact crystal agglomerate which was no longer hydroscopic would also have similar properties to coarse crystals, namely, that it would only dissolve slowly.

The product according to the present invention has, unexpectedly, only the advantageous properties and none of the disadvantages of fine and coarse crystals, respectively. The fructose product of this invention consists of readily flowable and friable coarse particles and contains virtually no fine material; it is substantially unaffected by atmospheric moisture and, therefore, does not become lumpy upon prolonged storage. On the other hand, the coarse particles are composed of many agglomerated finer particles, microcrystalline fructose units which separate rapidly when introduced into water and thus dissolve separately. Due to this separation of the larger particles into the smaller particles, the rate of dissolution of the fine crystals is retained, even after agglomeration. On the other hand, the agglomerates are so firm that, in the case of the usual mechanical stresses, such as arise in packing or sieving, they do not sutfer from attrition and do not break down to dust.

The following examples are given for the purpose of illustrating the present invention:

EXAM PLE 1 200 g. fructose, the fine part of which (particle size, i.e., average particle diameter, between 20 and 200 microns) amounted to 50-70 percent and which still con tained a residual moisture content of percent, based on fructose, of approximately 90 percent methanol in water, was spread out in a thin layer on a plate and dried with air at 60-80 C. in a circulating air cabinet. The fine material hereby agglomerated with the coarser crystals and the crystals, which were lightly caked together, could be converted, by sieving, into a 90 percent fraction with a particle size of 0.2-1.2 millimeters.

EXAMPLE 2 200 g. of starting fructose of the same composition and moisture content as in Example 1 were dried, with continuous movement, in a rotating, horizontal cylinder, using hot air with a temperature of 60-80 C. The quality of the product dried during movement thereof differed from that obtained according to Example 1 in that the caking together of the agglomerated crystals was avoided by the movement and the particles of the agglomerate were outstandingly spheroidal and of uniform size.

EXAMPLE 3 1.0 kg. fructose, the fine part of which amounted to 80 percent and which still contained a residual moisture content of about 4 to 5 percent by weight of 98 percent methanol (2 percent water) from the preceding crystallization, was the starting material. (The water content therein thus amounted to 0.08 to 0.10 percent, based on the weight of (dry) fructose.) This material was directly subjected to drying and the drying was carried out in such a manner that each charge was first pre-heated in a wobble drier to about 50 C. and subsequently dried in the usual way, either by blowing air therethrough or in a vacuum. The product obtained was practically free of very fine material with a size of 10-50 microns and 95 percent of it consisted of particles with a size of more than 0.1 millimeter.

EXAMPLE 4 5.0 kg. fructose of the same composition as in Example 3 were dried in a fluidized bed using hot air with a temperature of 60-80 C. until there was obtained the desired degree of dryness corresponding to a water content of less than 0.1 percent. Upon sieving this fructose, the proportion thereof with a particle size of more than 0.2 millimter was found to be about percent.

EXAMPLE 5 Into a continuously operating fluidized bed dried with a sufiiciently large fluidized bed surface, there were introduced, per hour, about 50 kg. fructose which, after the preceding centrifuging, still had a residual methanol content of about 5 percent and a water content of 0.8 percent, based on the fructose. The amount of air used, the temperature of which is 70-80 C., was kept down to such an amount that there was just obtained a suitable fluidized bed. In the case of a sufficiently long residence time (30 to 60 minutes), there was obtained a product with a moisture content of less than 0.1 percent water. The proportion of product with a particle size of more than 0.2 millimeter amounted to about 90 to percent.

EXAMPLE 6 A fructose which had been crystallized with a particularly high content of fine grained material was moistened with 4 to 5 percent of 90 percent aqueous methanol (10 percent water), based on fructose, and, with a continuous throughput, was dried in a plate drier at 70 C. to a residual water content of less than 0.1 percent. The residence time amounted to 30 to 45 minutes. The throughput amount depended upon the size of the plate drier used. The dried fructose obtained in this manner consisted of more than 95 percent of material with a particle size between 0.1 and 1.0 millimeter and consisted of about 90 percent of material with a particle size of between 0.2 and 1.0 millimeter. The fructose agglomerate thus obtained is particularly flowable, is resistant to attrition and is substantially insensitive to moisture, i.e., were non-hygroscopic. This product was particularly amenable to rapid dissolution.

What is claimed is:

1. Process for the production of an agglomerated anhydrous fructose having a particle size of 0.2 to 2.0 millimeters which comprises (a) moistening microcrystalline fructose consisting of crystals having a size of from 10 to 200 microns with an aqueous alkanol and,

(b) drying the moistened fructose at a temperature of from 40 to 90 C., wherein said aqueous alkanol weighs from 3 to 10 percent by weight based on the weight of the fructose and contains water in an amount of from 0.03 to 1.5 percent by weight based on the weight of the fructose, said alkanol having up to a 4 carbon atoms chain length.

2. Process as claimed in claim 1 in which the microcrystalline fructose starting material contains part of the water required for moistening.

3. Process as claimed in claim 1, wherein the microcrystalline fructose used as starting material has a particle size of 30 to microns.

4. Process as claimed in claim 1 wherein the water content is 0.1 to 1.0 percent by weight.

5. Process as claimed in claim 1 wherein the drying is carried out at a temperature of 70 to 80 C.

6. Process as claimed in claim 1 wherein the alkanol is methanol.

7. Process as claimed in claim 1 in which the aqueous alkanol contains the water and the alkanol-water mixture is used for moistening.

8. Process as claimed in claim 7 wherein the fructose is agitated during the drying.

9. Process for the production of agglomerated anhydrous fructose as claimed in claim 1 wherein the said microcrystalline fructose is initially obtained by crystallization and washing of said fructose with an aqueous alkanol which weighs from 3 to 10 percent by weight based on the weight of the fructose and contains water in an amount of from 0.03 to 1.5 percent by weight based on the weight of the fructose, said alkanol having up to a 4 carbon atom chain length, and said alkanol is used as the moistening alkanol of step (a) in claim 1.

10. Process as claimed in claim 9 wherein the drying is carried out in a fluidized bed.

11. Agglomerated anhydrous fructose having a particle size of 0.2 to 2.0 millimeters prepared by the process as claimed in claim 1.

References Cited UNITED STATES PATENTS MORRIS O. WOLK, Primary Examiner S. MARANTZ, Assistant Examiner US. Cl. X.R.

99-Digest 4; 12758, 63 

